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On Site Guide intelligence

Pirform's intelligence incorporates the following guidance from the IET's On-Site Guide, specifically Table 7.1(ii). Read more here.

Ring Final Circuits

The following ring final circuits configurations are recognised by cable-sizing rules.

Rating Standard Live CPC Reference Method TN-S 30 mA RCD TN-S No RCD TN-C-S 30 mA RCD TN-C-S No RCD
30 3036 2.5 1.5 100, 102, A, C 106 41zs 106 106
30 3036 4 1.5 100, 102, A, 101, 103, C 171 48 171 138zs
32 CB (60898 B, C, & D) 2.5 1.5 100, 102, A, C 106 96zs 106 106
32 RCBO (61009 B, C, & D) 2.5 1.5 100, 102, A, C 106 NPzs 106 56zs
32 88-2 2.5 1.5 100, 102, A, C 106 NPzs 106 NPzs
32 60269-2 2.5 1.5 100, 102, A, C 106vd 32zs 106vd 106vd
32 88-2 4 1.5 100, 101, 102, 103, A, C 171 38zs 106vd 127zs
32 60269-2 4 1.5 100, 101, 102, 103, A, C 106vd 19ad 106 95zs
32 88-3 2.5 1.5 100, 102, A, C 171 22zs 171 112zs
32 88-3 4 1.5 100, 101, 102, 103, A, C 171vd 114ZS 171vd 171vd
32 CB (60898 B, C, & D) 4 1.5 100, 101, 102, 103, A, C 171vd NPzs 171vd 66zs
32 RCBO (61009 B, C, & D) 4 1.5 100, 101, 102, 103, A, C 171vd NPzs 171vd NPzs

The following abbreviations are used in the table above:

  • CB: Circuit breaker
  • RCBO: Residual current circuit breaker with overcurrent protection
  • TN-S: Terra neutral - separate
  • TN-C-S: Terra neutral - combined and separate
  • RCD: Residual current device
  • vd: Voltage drop
  • ad: Adiabatic limit
  • zs: Earth fault loop impedance
  • sc: Line to neutral
  • NP: Not permitted
  • NPvd: Not permitted (prohibiting factor: voltage drop)
  • NPad: Not permitted (prohibiting factor: adiabatic limit)
  • NPzs: Not permitted (prohibiting factor: earth fault loop impedance)
  • NPsc: Not permitted (prohibiting factor: line to neutral)